Over decades, worldwide space communities have dreamed a new launching system that can be used like car, ship or airplane, providing human beings a low-cost, reliable and convenient access into space. A plethora of concepts therefore have been proposed, technologically and economically scrutinized, blueprinted or even reduced into practical trial. However, to date, the realization of that great dream yet has a long way to go.
Current orbital payload launching systems in service and those that will probably become operational in near future, approximately fall into two categories: The first and the primary category, is using a conventional ground-launched rocket, such as Saturn V, Delta, Atlas, R-7, Proton, Ariane, Long March and H2B; The other category employs a so-called hybrid technology, that is, lifting the launch of a conventional rocket or other kind of vehicle to a predefined altitude via a launch platform, typically an airplane, and then launching that rocket or vehicle.
Today, the usage of conventional ground-launched rocket is wide and sophisticated. However, this method suffers limitations, mainly the high cost per unit payload mass and a large amount of preparation work required prior to each mission, which hurdle the large scale scientific exploration and commercial exploitation in space. Therefore, a series of novel technical routes have been suggested and tried, to overcome these limitations.
Besides the efforts to reuse parts of conventional ground-launched rocket to lower the cost, such as the recently retired space shuttle and the reusable first stage under development by SpaceX, other approaches of launching payload into space orbit have also been proposed, and some even went into practise, for instance, the Pegasus rocket launched by B-52, and more recently, the Stratolaunch founded by Paul G. Allen and Burt Rutan. They all follow the idea that bring the launch of rocket/vehicle to a predefined high altitude, taking advantages of high-altitude launch, and thus lowering time and money expenditure of each mission.
High-altitude launch, or air launching, generally confers advantages over conventional ground lift-off in the following ways:                (i) increases thrust and specific impulse (Isp) of rocket engine: Ambient pressure at high altitude is much lower than the sea level. As such, back-pressure is greatly reduced. Rocket engine thrust and specific impulse both receive a substantial gain. Besides, because the low ambient pressure greatly minimize the overexpansion problem, rocket engine designers thereby own a larger flexibility to chose a larger expansion area ratio and further increase rocket engine thrust and specific impulse;        (ii) reduces steering loss and gravity drag: high altitude launch makes it permissible that the rocket/vehicle flies at a pitch closer to horizontal in initial stage, which grants more flexibilities to trajectory optimization, and hence reducing steering loss and gravity drag. Besides, the rocket/vehicle also owns potential to take advantage of aerodynamic lifting force to counter the gravity.        (iii) reduces the aerodynamic drag and Max-Q: the high altitude launch avoids travelling through the dense portion of atmosphere and thereby reduces the amount of fuel wasted by aerodynamic drag, and minimizes the maximum dynamic pressure;        (iv) allows a lower thrust/weight ratio at ignition;        (v) avoids the destructive acoustical energy that is reflected by ground surface in the conventional lift-off;        
However, two high-altitude launch approaches that have been put into practise, launching from an airplane and from a balloon, both unfortunately suffer critical constrains or drawbacks. The approach that launching a rocket/vehicle from an airplane, is greatly constrained by the maximum payload capacity and available volume of its carrier airplane. Launching a mainstream communications satellite or spaceship using this approach is not feasible because there is no operational airplane with the required payload and volume capacity. Meanwhile, the launching-from-balloon approach suffers a critical drawback that the balloon is lack of steerability. As such, the delta-v penalty would be large to compensate positional and azimuth error that brought by balloon. The unpredicted free falling of rocket/vehicle debris additionally raises safety concerns. Moreover, the balloon is not reusable and hence increases the cost. These drawbacks render the balloon launching approach still staying in tentative suborbital usage today, albeit the first launching from balloon took place over half century ago (Rockoon was started in 1950s).
In view of this, while inherit the basic idea of high-altitude launch, the present invention avoids the aforementioned constrains and drawbacks based on recent advances in high-altitude airship and novel features that will be introduced in the following sections.
The complete retirement of space shuttle fleet in 2011 s a huge setback for space community. However, that doesn't weaken the fact that the space shuttle program is thus far one of the greatest achievements in human space exploration and exploitation. The stratospheric-launched suborbital shuttle (SLSS) in the present invention is based on technologies and hardware of space shuttle, and lessons learned in the space shuttle program. Unlike space shuttle that rockets directly into a low earth orbit (LEO), the SLSS releases its cargo at an altitude just above the atmosphere and on a speed lower than the orbital speed, in order to lower the complexity and structural weight required for re-entry, increase the overall payload capacity, and make the SLSS more durable, reliable and much easier to build. Besides, albeit SLSS can be used in manned mission in the future, it is an unmanned vehicle. The weight and complexity of a pressurized cabin and life support system thus can be saved.
Together with an airship-based stratoshperic launch platform, a SLSS and an upper stage (a modified version of conventional upper stage or a newly developed spaceplane), the present invention constructs a novel orbital payload launching system, which has the potential to achieve the lowest cost ever, the highest reusability ratio and reliability, at one stroke.